that's extremely vague... there are so many aspects and directions you can take even a simple CMS... what type of data will you be needing to control? give us an idea of what your simple cms is going to handle, and we'll be able to help much more efficiently.

You can't win, you can't lose, you can't break even... you can't even get out of the game.

Better yet, take a look at the site http://www.opensourcecms.com which not only has news information and links to the major PHP based cms systems, forums and wikis, but also has demos of them installed that you can play with.